A week or two ago, I was struck with the inspiration to write up a class where you can play as a vehicle. Despite the many challenges I faced, I'd like to think I didn't do too badly.

Link: https://docs.google.com/document/d/1...it?usp=sharing

Forum-quotable no-fluff version under spoiler (please see above link for the most up to date version):
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The Living Dreadnought
  1. Iron Turret
  2. Scout Class Dreadnought, Transport, 4 mph
  3. Dreadnought Division, 4 mph
  4. Ability Score Improvement, 4 mph
  5. Extra Attack, Expedition Class Dreadnought, 6 mph
  6. Dreadnought Division feature, Cold Iron Shells, 6 mph
  7. Burning Rubber, 6 mph
  8. Ability Score Improvement, 6 mph
  9. Iron Bombardment, 8 mph
  10. Dreadnought Division feature, 8 mph
  11. Praetor Class Dreadnought, Iron Barrage, 8 mph
  12. Ability Score Improvement, 8 mph
  13. Dardanelles Gun, Fortified Deck, 10 mph
  14. Dreadnought Division feature, 10 mph
  15. Impervious Hull 10 mph
  16. Ability Score Improvement, 10 mph
  17. Titan Class Dreadnought, Dread Nought, 12 mph
  18. Steel Artillery, 12 mph
  19. Ability Score Improvement, 12 mph
  20. Automated Crew, 12 mph

Multiclassing
Prerequisites: CON 13
Proficiencies: simple weapons, martial weapons, light armor, medium armor, shields

Class Features
As a living dreadnought, you gain the following class features.

Hit Points

Hit Dice: 1d12 per class level
Hit Points at 1st Level: 12 + your Constitution modifier
Hit Points at Higher Levels: 1d12 (or 7) + your Constitution modifier per class level after 1st

Proficiencies

Armor: Light armor, medium armor, heavy armor, and shields
Weapons: Simple weapons, martial weapons, firearms
Tools: none

Saving Throws: Strength, Constitution
Skills: Choose two from Athletics, Acrobatics, History, Intimidation, Medicine, Perception, and Stealth

Equipment

You start with the following equipment, in addition to the equipment granted by your background:
  • Any simple or martial melee weapon
  • (a) a shield, or (b) any ranged simple or martial weapon
  • (a) leather armor, (b) scale mail, or (c) chain mail
  • (a) an explorer’s pack, or (b) a dungeoneer’s pack

Iron Turret
Beginning at 1st level, your body has fused with the core of a terrible engine of destruction. This dreadnought core begins to reshape your body into a machine of war, creating one or more cannons that are fused with your body. You determine the appearance of the cannons, and can retract them back into your body to conceal them. Your body might also begin to take on other aspects of the dreadnought core, such as metal plates or mechanical body parts.

You may use your iron turrets in three different ways.

Natural Weapon. Your iron turrets are a natural weapon that you may use as a simple ranged weapon in which you are proficient with the finesse property and a range of 20/60 feet. The turret deals 1d6 piercing damage on a hit.

Any time you make an unarmed strike, you may instead attack using your iron turret.

Note: This mostly applies to monks operating a battle station, allowing them to use the turret with their Martial Arts bonus action attack and with Flurry of Blows.

Weapon Enhancement. Each turret contains a slot that a weapon can be inserted into. The cannon will reconfigure itself to use that weapon’s properties. Once per turn, you may use the turret this way when you attack with a weapon you are wielding, enhancing that attack in the following ways:
  • The weapon deals additional damage equal to the turret’s damage die.
  • The weapon’s range increases to 20/60 feet, if it was less than that. Melee weapons still use a melee attack, unless that weapon has the thrown property, in which case you may choose whether it is a melee or ranged attack. If a weapon has the thrown property, you can use its thrown range without throwing the weapon.
  • You may ignore the ammunition property of the weapon, if it has it, as your body manufactures its own ammunition. You may still load special ammunition into the weapon if you wish.

Once you reach 5th level in this class, you are no longer limited to only using this feature once per turn.

Spell Enhancement. Spells can be channeled through the turret to increase damage and range. When you cast a spell, you may use the turret to enhance that spell in the following ways:
  • One of the spell’s damage rolls deals additional damage equal to the turret’s damage die.
  • The spell’s range increases to 30 feet if it was less than that. Spells that use their range to define the area of the spell’s effect, such as those that radiate out from the caster, can’t use this benefit.
  • You may use the turret as a spellcasting focus for the spell.

Once you reach 5th level in this class, you may add the turret’s damage die to all of the spell’s damage rolls.

Scout Class Dreadnought
Starting at 2nd level, the dreadnought core can construct a scout class dreadnought. As an action, you can transform into a scout class dreadnought, or back into your original form. You determine the appearance of your dreadnought forms. Except as noted, you have the same statistics in either form.

While in your scout class form, you gain the following benefits.
  • Your size is medium.
  • Your iron turret’s damage die is 1d6 (same as your original form).
  • You have one battle station.

While in any dreadnought form, you can carry up to 200 lbs. inside your extradimensional space. You can also carry one passenger. If you exceed these limits, the overflow counts against your encumbrance.

Your dreadnought form is considered a construct and is immune to poison. You retain your original creature type while in your original form, but creatures inside your extradimensional space can only interact with your dreadnought form.

You can find more rules for your dreadnought forms at the end of this document.

Transport
Beginning at 2nd level, you may be used as a vehicle for long distance travel. You can continue to travel even while asleep, though you’ll move in a straight line unless a creature operating a battle station is steering you. You also don’t suffer any negative effects for taking a forced march.

While in a dreadnought form, you can travel at a pace of 4 mph. This is considered a normal pace. As your level in this class increases, your travel pace increases, as shown in the Travel Speed column of the Living Dreadnought table.

Even though you can swim or climb without a swim or climb speed, you aren’t able to do so competently over long distances as required when traveling. In order to travel over certain types of terrain, such as across the sea, up mountains, or through the air, you need the appropriate type of move speed.

Dreadnought Division
When you reach 3rd level, you specialize your dreadnought design into one of three divisions: the tunneling Behemoth, the oceanic Leviathan, or the airborne Garuda. Your choice of division grants you features at 3rd level, and additional features at 6th, 10th, and 14th level.

Ability Score Improvement
When you reach 4th level, and again at 8th, 12th, 16th, and 19th level, you can increase one ability score of your choice by 2, or you can increase two ability scores of your choice by 1. As normal, you can’t increase an ability score above 20 using this feature.

Extra Attack
Beginning at 5th level, you can attack twice, instead of once, whenever you take the Attack action on your turn.

In addition, when you or a creature operating a battlestation uses your turrets to enhance a weapon, they may do so any number of times instead of just once per turn. Likewise, when they may enhance all of the damage rolls of a spell, instead of just one.

Expedition Class Dreadnought
When you reach 5th level, your dreadnought core can now transform you into an expedition class dreadnought. While in your expedition class form, you gain the following benefits.
  • Your size is large.
  • Your iron turret’s damage die is 1d8.
  • You have two battle stations.
  • Your expedition class form has armor plating that reduces all damage taken by 3.

While in any dreadnought form, you can carry up to 10 tons inside your extradimensional space. You can also carry up to 5 passengers. If you exceed these limits, the overflow counts against your encumbrance.

You can also use your dreadnought core’s extradimensional space to fold up your body, allowing you to revert to a smaller dreadnought class. When you use your action to transform, you can take the form of any dreadnought class you’ve unlocked, or revert to your original form.

Cold Iron Shells
Starting at 6th level, attacks made using your iron turrets count as magical for the purposes of overcoming damage resistance and immunity. This includes both using the turret as a natural weapon, and using it to enhance a weapon.

Burning Rubber
Once you reach 7th level, your movement speed increases by 10 feet.

Iron Bombardment
Starting at 9th level, you can unleash a barrage of explosive shells from all your cannons as an action. Choose a point within 120 feet. Creatures within a cube must make a Dexterity saving throw, with a DC equal to 8 + your Strength or Dexterity modifier + your proficiency bonus. On a failure, they take bludgeoning damage equal to three rolls of your iron turret damage die. The size of the cube depends on the class of your dreadnought form: a 5-foot cube for scout class, a 10-foot cube for expedition class, a 15-foot cube for praetor class, and a 20-foot cube for titan class. If you are not in a dreadnought form, use a 5-foot cube.

Praetor Class Dreadnought
When you reach 11th level, your dreadnought core can now transform you into a praetor class dreadnought. While in your praetor class form, you gain the following benefits.
  • Your size is huge.
  • Your iron turret’s damage die is 1d10.
  • You have six battle stations.
  • Your praetor class form has armor plating that reduces all damage taken by 6.
  • The range of your iron turret, iron bombardment, and Dardanelles gun is doubled. This also doubles the range of weapons or spells enhanced by your turrets. The range of your special senses is also doubled.
  • Your reach increases by 5 feet.

While in any dreadnought form, you can carry up to 1000 tons inside your extradimensional space. You can also carry up to 40 passengers. If you exceed these limits, the overflow counts against your encumbrance.

Iron Barrage
Once you reach 11th level, you can shoot your iron turret as a bonus action, using the natural weapon option.

Dardanelles Gun
Starting at 13th level, you incorporate a massive cannon into your dreadnought frame. One blast from this cannon is devastating, but it is unwieldy and unsafe.

As an action, you may expend any number of hit dice to add them to the cannon’s damage dice pool. On each subsequent turn until the cannon is fired, you must spend an action to either charge up the cannon, or to fire the cannon. If you fail to do so, the stored energy becomes unstable and explodes. Roll the dice pool and take that much force damage.

When you use an action to charge up the cannon, it doubles the dice in its dice pool. When you use an action to fire the cannon, each creature in a line that has a length of 600 feet and a diameter of 10 feet must make a Dexterity saving throw, with a DC equal to 8 + your Constitution modifier + your proficiency bonus. Roll the dice in the pool, and targets who fail their saving throw take force damage equal to the amount rolled, or half as much on a successful saving throw. The cannon is so powerful that the blast also damages you, causing you to take half the damage rolled.

In addition to damaging creatures, the cannon will also destroy objects and structures caught in the blast. If an object or structure is capable of making a Dexterity saving throw, it may do so to take half damage on a success, otherwise that object or structure takes the full amount of damage as if it had failed the saving throw.

Fortified Deck
Starting at 13th level, passengers on the deck, including those operating battle stations, have half cover against anything outside. You also gain a +2 bonus to contested ability checks to prevent someone from boarding or disembarking.

Impervious Hull
Beginning at 15th level, you gain resistance to bludgeoning, piercing, and slashing damage.

Titan Class Dreadnought
When you reach 17th level, your dreadnought core can now transform you into a titan class dreadnought. While in your titan class form, you gain the following benefits.
  • Your size is gargantuan.
  • Your iron turret’s damage die is 1d12.
  • You have 24 battle stations.
  • Your titan class form has armor plating that reduces all damage taken by 12.
  • The range of your iron turret, iron bombardment, and Dardanelles gun is tripled. This also triples the range of weapons or spells enhanced by your turrets. The range of your special senses is also tripled.
  • Your reach increases by 15 feet.

While in any dreadnought form, you can carry up to 100,000 tons inside your extradimensional space. You can also carry up to 2000 passengers. If you exceed these limits, the overflow counts against your encumbrance.

Dread Nought
Once you reach 17th level, you become an implacable machine of destruction, one which dreads nothing at all. You are immune to the frightened and charmed conditions.

Steel Artillery
When you reach 18th level, the range of all your ranged attacks, weapons and spells enhanced by your iron turrets, your iron bombardment, and your Dardanelles gun are doubled.

Automated Crew
When you reach 20th level, you can manufacture constructs that are capable of operating battle stations. These constructs cannot leave your dreadnought form, and must stay in the extradimensional space inside the dreadnought core. You can have up to 20 automated crewmen at a time, which do count against the number of passengers you can carry. You can rebuild two automated crewmen at the end of a short rest, or all automated crewmen at the end of a long rest.

You have a telepathic link with your automated crewmen that allows you to be aware of anything they perceive, as well as issue commands to your automated crewmen. Your automated crewmen act on your turn. To make combat run more quickly and smoothly, choose the actions for your automated crew all at once, and then roll and all attack rolls simultaneously, and likewise for damage rolls.

Your automated crewmen use the following stat block.

(AC 14, HP 20, Speed 30, STR/DEX/CON 14, INT/WIS/CHA 8, proficiency +3, see link for more details)

Dreadnought Behemoth
Blitzkrieg
When you choose this dreadnought division at 3rd level, your walking speed increases by 10 feet, or increases to 40 feet, whichever is higher. In addition, you may ignore the effects of difficult terrain, and your speed can’t be reduced except by effects that reduce your speed to 0.

You also gain proficiency with vehicles (land).

Steamroll
Beginning at 3rd level, you can attempt to roll over smaller creatures to knock them prone and damage them. When you move through the space of a creature at least two sizes smaller than you, that creature must succeed on a Dexterity saving throw with a DC equal to 8 + your Strength modifier + your proficiency bonus, or else they are knocked prone. Moving through a prone creature’s space causes that creature to take bludgeoning damage equal to two rolls of your iron turret damage die. Once you’ve dealt damage to a creature in this way, you can’t damage a creature this way again until the start of your next turn.

Earth-Moving Machine
Starting at 6th level, you are equipped with drills and other equipment to help you traverse both over and under terrain. You gain a climbing speed equal to your walking speed, and a burrow speed equal to half your walking speed. You can only burrow through dirt, mud, sand, and other soft materials. You leave a tunnel behind you as you burrow.

Seismic Senses
Beginning at 10th level, you gain tremorsense out to 60 feet.

Heaven-Piercing Drill
Once you reach 14th level, you can now burrow through most types of stone as well as dirt.

Your burrowing abilities are now sufficient to sustain long distance travel. While traveling by burrowing, you move at half your normal rate of travel.

Dreadnought Leviathan
Seaworthy
When you choose this dreadnought division at 3rd level, you gain a swim speed equal to your walking speed. If you already have a swim speed, that swim speed increases by 10 feet, and you may use whichever is higher.

You also gain proficiency with vehicles (water).

Ramming Prow
When you reach 3rd level, you reinforce the front of your dreadnought forms so you can ram into enemies without harming yourself (you don’t need to be in a dreadnought form to use this feature). If you move at least 20 feet in a straight line into a space adjacent to another creature, you can ram that creature. The target must make a Strength saving throw, taking bludgeoning damage equal to two rolls of your iron turret damage die on a failed saving throw. This damage increases by one roll of your iron turret damage die for every additional 10 feet you move in a straight line, up to a maximum of ten rolls of your iron turret die.

Once you use this feature, you can’t use it again until the start of your next turn.

Sonar
Once you reach 6th level, you can emit sound waves that help you to see your surroundings. You gain blindsight that extends out to 60 feet in water and other liquids, and out to 10 feet in other mediums. You can’t use this blindsight while deafened.

Submersible
Starting at 10th level, you can manufacture breathable air for yourself and your passengers. In addition, you can create a soap-like film that creates an air-tight seal around your interior, allowing you to dive underwater while keeping the interior dry. Attacks and other objects and effects can pass through the soapy film without damaging it or being affected by it.

In addition, you can pipe air through flexible tubes to any number of creatures up to 120 feet away from you. Each tube is equipped with a mouthpiece that a creature can don as an action, allowing that creature to breathe, even while under water or in spaces without breathable air. The tubes have 5 hit points and an AC of 12.

Silent Running
Beginning at 14th level, you are able to mute all sound produced within you. As an action, you can enable silent running mode, which creates a soundproof barrier between yourself and the outside world. You and your passengers are deafened to anything outside, but anything outside is also deafened to you and your passengers. You can turn off silent running mode as a bonus action.

Dreadnought Garuda
Powered Jump
When you choose this dreadnought division at 3rd level, your high jump height increases by 10 feet and your long jump distance increases by 20 feet.

You also gain proficiency with vehicles (air).

Dogfighter
Starting at 3rd level, the base range of your iron turret is extended to 30/120 feet. When your iron turret enhances a weapon, that weapon’s range increases to 30/120 feet, if it was less than that. An enhanced spell with a range of touch or at least 10 feet has its range increased to 60 feet if it was less than that.

Sky Ship
Beginning at 6th level, you gain a fly speed equal to your walk speed. If you already have a fly speed, that fly speed increases by 10 feet, and you may use whichever is higher.

Bomber
When you reach 10th level, when you use your iron bombardment, you can opt to drop bombs instead of firing your cannons. By doing so, you can target a point up to 30 feet away horizontally, but up to 600 feet below.

Eyes of the Ace
Once you reach 10th level, you gain the eyesight of an eagle. You can see up to 1 mile away with no difficulty, able to discern even fine details as though looking at something no more than 100 feet away from you. Additionally, dim light doesn't impose disadvantage on your Wisdom (Perception) checks.

Spelljammer
Starting when you reach 14th level, you become able to travel among the stars. You can safely enter and exit the atmospheres around planets and travel through the space between them. While outside of a planetary atmosphere, you can accelerate to the much higher speeds needed to travel between planets in a timely manner.

In some settings, space contains breathable air. If your setting does not, then you can maintain a breathable atmosphere on board yourself. This doesn’t prevent anything else from getting in or out, however. If you dive underwater or travel through poison gas, those will leak inside of you.

Dreadnought Form Rules
Your dreadnought transformation is a rather unusual concept, and as such requires a few more rules to handle it elegantly than most class features. Those rules have thus been compiled here so as not to bog down the class description, and also to make it easier to refer back to this section for all the rules of your dreadnought forms instead of distributing them between several class features.

Constructed Nature
Your dreadnought form counts as a construct, while your original form retains its original creature type. While you are in your dreadnought form, your original form can’t be targeted at all, and creatures who are aboard you or inside your extradimensional space can only target your dreadnought form.

Your dreadnought form is immune to poison, including poison damage and the poisoned condition.

Although the dreadnought itself is a construct, it is still fused with your body, which is still flesh and blood. As such, you must still fulfill your biological needs as normal. You can manifest your original form inside your extradimensional space, but only while in your dreadnought form (your original body can’t be in two places at once). This allows you to eat and drink while in your dreadnought form.

If you manifest your original form inside the extradimensional space, it can be targeted and is treated as your original creature type. For example, a caster could cast cure wounds, which doesn’t normally affect constructs, on your original form to heal you. Manifesting your original form requires an action, and you can’t make your dreadnought form move (except forward in a straight line, as if you were sleeping) or take actions until you use an action to return your original form into the dreadnought.

Size and Appearance
You determine the appearance of each of your dreadnought forms, including your size. This doesn’t change your size category, and often your physical size will be larger than the space you occupy. For example, a praetor class dreadnought leviathan could be around 40 feet long, the length of a typical mid-sized warship, while a titan class dreadnought leviathan might exceed several hundred feet in length. Unfortunately, this means there will be a discrepancy between the space you occupy according to the rules and how large you describe that form as being. This is necessary for game balance reasons; work with your DM to find adequate ways of describing how this looks in combat.

Passengers and Boarding
You’re able to carry a certain number of passengers, which doesn’t count against your encumbrance. As you unlock larger forms, this number increases, regardless of what form you’re in. This limit is based on accommodating medium sized creatures. A large creature counts as 2 passengers, a huge creature counts as 4, and a gargantuan creature counts as 8. Conversely, 2 small creatures count as only one passenger. You don’t usually need to keep track of tiny creatures, though if you try to carry an unreasonable number of tiny creatures then the DM may count 4 tiny creatures (rounded down) as 1 passenger. You may carry passengers beyond these limits, but those passengers will count against your encumbrance.

A creature in an adjacent space can board you by spending half their movement. A creature that is aboard you may spend half their movement to disembark, causing them to appear in an adjacent unoccupied space.

When a creature tries to board or disembark from you, you may use a reaction to try and prevent them from doing so. Make a contested ability check using your choice of Strength (Athletics) or Dexterity (Acrobatics) against the boarding creature’s Strength (Athletics) or Dexterity (Acrobatics) (their choice). If the boarding/disembarking creature wins, it comes aboard or disembarks, and if you win or tie, then that creature can’t board you or disembark on that turn.

A creature can only board or disembark while you are in a dreadnought form. If a creature has the ability to teleport, such as with a spell, they can attempt to teleport out of your extradimensional space if you are not in a dreadnought form. The creature must succeed on a Charisma saving throw with a DC equal 8 + your Constitution modifier + your proficiency bonus, or else the teleportation fails. (At the DM’s discretion, this may simply cause the teleportation to fail, or the creature may teleport to a random location inside the extradimensional space.)

Battle Stations
Each form has a number of battle stations that a passenger can operate. All battle stations are equipped with the same facilities. A creature operating a battle station may use it in any of the following ways:

Gunner
Each battle station is equipped with an iron turret. The creature operating a battle station may use the turret in the same way you can, attacking with it as a natural weapon or using it to enhance a weapon or spell.

Pilot
When a creature operating a battle station takes the Dash action, they may instead choose to direct you to move up to your movement speed during their turn. They can break up your movement between their other actions, as if they were the ones moving.

When a creature operating a battle station takes the Disengage action, they may instead choose to impose disadvantage on opportunity attacks made against you until the start of their next turn.

When you are hit by an attack or fail a Dexterity saving throw, a creature operating a battle station may use their reaction to direct you to evade, granting you a bonus to your AC against that attack or to that Dexterity saving throw equal to their Dexterity modifier.

Engineer
A creature operating a battle station can choose to treat you as the origin of effects that normally treat themselves as the origin of that effect. For example, a paladin’s auras or the thunderclap spell can emanate from your space instead of the user’s space.

Each battle station is also equipped with hooks, cranes, grabbers, claws, or similar. If you are in a dreadnought form that grants an increase to your reach, creatures operating a battle station get the same increase to their reach.

Targeting and Navigation
You can share your senses, including special senses, with creatures operating battle stations. As an action, you can allow all creatures operating a battle station to perceive through your senses until the start of your next turn. You can also use a reaction during the turn of a creature operating a battle station to share your senses with that creature until the end of their turn.

Extradimensional Space
The dreadnought core contains an extradimensional space. All of your dreadnought forms which you’ve unlocked are a part of your body simultaneously. You can revert to a smaller form, or back to your original form, by folding your body into that extradimensional space, storing your larger forms inside until you need them again.

You can store objects within the extradimensional space. As you unlock larger forms, the amount of weight you can carry in the extradimensional space increases, even while in a smaller form. Each dreadnought form specifies how much it expands the space. The weight you carry in the extradimensional space doesn’t count against your encumbrance. However, if you exceed the limit, then the excess will count against your encumbrance.

Transforming in Confined Spaces
When you transform into a dreadnought form and there are creatures in the space occupied by your new form, you may choose to safely bring those creatures aboard, if you have enough room to accommodate them. If you choose not to bring a creature aboard, or are unable to, you instead push them in a straight line away from you until they either reach an unoccupied space or are stopped by an obstacle. The creature must make a Dexterity saving throw with a DC equal to 8 + your Constitution modifier + your proficiency bonus, which the creature automatically fails if they are pressed up against an obstacle. On a failure, the creature takes 1d6 bludgeoning damage for every 5 feet it was pushed.

If you transform into a dreadnought form and there isn’t enough unoccupied space, you can attempt to force the transformation. You can push objects out of the way, but obstacles such as trees or walls need to be destroyed in order to transform successfully. If you choose to force the transformation, then the DM will determine how much bludgeoning damage is required to destroy enough of the environment in order to create the space required for your new form. You then take the same amount of bludgeoning damage. As a reaction, after you find out how much this damage will be, you can either stop the transformation or take a smaller form instead. If you do so, you and the environment still take half the damage.

Interior and Layout
You determine the appearance of each of your dreadnought forms, but we can broadly divide the spaces inside you into three different types: the exterior decks, the interior cabins, and the interior holds. Note that these terms might not refer to literal decks, cabins, or holds, these are just to help differentiate between the different types of spaces inside you.

The deck is an exterior space where creatures can board or disembark from. Passengers on the deck are exposed, both able to see and be seen by creatures outside, and able to attack and be attacked by the same. Your battle stations are all on the deck. Creatures may only board onto the deck and disembark from the deck.

Cabins and holds are both enclosed interior spaces that create full cover between passengers inside those spaces and anything outside of you. The difference between cabins and holds is that cabins connect directly to the deck, allowing passengers on the deck to see and interact with passengers in cabins, and vice versa. Holds, on the other hand, cannot be accessed directly from the deck, and must be accessed through a cabin.

You may create your own map for the layout of your dreadnought form, mapping out the deck and individual interior rooms and hallways. This is not required, however. If you choose not to do so, then you may use the following abstraction:

Using an abstract layout, you have one central deck. Connected to that deck are an arbitrary number of cabins. Connected to each cabin are an arbitrary number of holds. A creature may move from one space to a connected space by spending all their movement; a Dash action can be used to move again to a second connected space. When a creature enters a cabin from the deck, they may choose to enter the same cabin as another creature already inside a cabin, or to enter an unoccupied cabin. Likewise, when a creature enters a hold, they may choose to enter a connected hold occupied by another creature, or to enter an unoccupied hold, which is connected to that cabin. Creatures in the same space are considered to be close enough to use melee weapons and touch spells, but aren’t penalized for using ranged weapons. When moving from one space to another, you provoke opportunity attacks from creatures in the space you are leaving, however, only one creature can make an opportunity attack against you.

As you unlock larger forms, your extradimensional space grows. You only have one layout for your dreadnought form; if you are currently in a smaller form, then part of your interior is folded up into the extradimensional space. Creatures who are aboard you won’t notice anything different, as they can freely enter and exit the extradimensional space as if you were always in your largest form. While on the deck they may notice that the view of the exterior is partially blocked by other parts of the dreadnought folding back on itself, with only part of the deck visible to the outside. If you revert to your original form, then those looked outside of the dreadnought will only see other parts of the dreadnought folding in on itself, completely blocking off the outside.

Immutable Form
While you are in a dreadnought form, you are immune to any spell or effect that would alter your form, aside from your dreadnought features. While in your original form, you can still be affected by spells or effects that would alter your form.

While you have some ability to flex and reshape your dreadnought form, it is not as soft and malleable as organic flesh. This prevents you from squeezing while in a dreadnought form. Since most dreadnoughts are physically bigger than the space they occupy, “squeezing” for them is closer to fitting through spaces as wide as the space you occupy, e.g. a titan class dreadnought fitting through a space 20 feet wide.

Abandoning and Rebuilding your Shell
With larger forms comes greater danger, as you become a bigger target. As such, you can choose to abandon a dreadnought form in a desperate situation. When you are reduced to 0 hit points and you are in an expedition class or larger form, you may choose to abandon that form. The shell becomes a nonfunctional object. You immediately stabilize and can choose to appear on board the shell, if there is enough passenger space to accommodate you, or in the nearest unoccupied space.

Shedding a dreadnought shell has consequences. You no longer have access to any dreadnought form except your scout form, nor do you gain any of the benefits of your other forms, including the increased carry capacity or passenger space. You can rebuild a discarded dreadnought form with enough time and materials. You must rebuild a smaller form before you can rebuild a larger form. Because your larger forms are built around your smaller forms, discarding a smaller form will prevent you from transforming into your larger forms until the smaller form is rebuilt, though the larger forms will not need to be rebuilt.

The time and cost of materials required to rebuild a dreadnought form depends on the form. You can rebuild your expedition class form at the end of a long rest using 1,000 gp worth of materials. Rebuilding your praetor class form requires 1 week of work and 10,000 gp worth of materials. Rebuilding your titan class form requires 4 weeks of work and 100,000 gp worth of materials. If you reclaim the discarded shell, you can use that shell as the materials to rebuild all discarded forms. You can also scavenge suitable materials, typically wood, metal, or stone, such as the discarded weapons and armor of defeated enemies, or the structures of defeated enemies.

Quick Summary:
This is a 100% pure martial class, no spells (not enough of those, honestly). You can turn into a vehicle, with larger variants unlocking at higher levels. It comes with three subclasses: the drill tank, the amphibious submersible, and air/spaceship. Party members can crew turrets that enhance their weapons and spells, allowing them to use most of their class features. Most of your firepower comes from your crew; by yourself, you're actually probably weaker than most other PCs. Think of this as a support class.

Something you'll notice is that each tier gives a clear progression that fits very well with your identity as the party transport:
  • In tier 1 you are someone's personal mech suit. You're not really that useful as a vehicle.
  • In tier 2, you can now carry the entire party, so you can act as a transport. There isn't much room for anything else, though.
  • In tier 3, you're now roomy enough to act as a small mobile base for the party.
  • In tier 4, you're now a massive stronghold. A moving castle, if you will.

While designing this class, there were a number of issues I had to overcome. Being aware of these can help inform you as to why I made some of the questionable decisions that I did. Ultimately, I had to strike a compromise between fulfilling the concept and being game balanced.

Size and Confined Spaces
You can't very well bring your airship into the dungeon, now can you? In order to allow you to follow your party into confined spaces, I felt it necessary to allow you to switch between any of your sizes, or turn back into your original form, rather than forcing you to always use your largest form. It was a pretty simple fix, but harder to justify. The extradimensional space is the justification for how this is possible.

Balance vs. Power Fantasy
We expect ship-to-ship battles to be high powered stuff. The idea of a PC 1v1'ing a battleship is a bit ridiculous. So I needed this class to be strong enough to do ship-to-ship battles justice, while also being balanced for dungeons crawls and other small-scale stuff. The way I tried to achieve this is by leveraging size. Dungeons won't often have enough space for you to use your larger forms, requiring you to take only your smaller forms. On the other hand, any time you're engaged in combat with an enemy vessel, you will undoubtedly have enough space to assume your largest form. Larger forms give a few crucial benefits, with the biggest being more turrets that can be crewed. Simply being bigger isn't enough; you need other people to crew those turrets, and if you have the necessary crew, you can fulfill that power fantasy of engaging ship-to-ship combat.

In the end, there was never going to be a way to achieve perfect balance, but if the DM is able to control what form the dreadnought player can use, then they can adjust the power level to suit the particular scenario.

Party Involvement
The last thing I wanted was for the rest of the party to be sitting on their hands while you 1v1 an enemy vessel in ship-to-ship combat. Therefore, I tried to get the rest of your party as involved as possible through the battle station system. These allow your party to use most of their class features while they are manning a turret, even features like Cunning Action or Flurry of Blows.

Please share any feedback, though do be aware that with the nature of this class, there's only so much I can change before it no longer fulfills its intended concept. This class will never be right for every table, so my hope is that at least some tables will be able to look past the flaws and have fun. What I'm saying is that just because I don't follow your advice, it doesn't mean that you're actually wrong in your critique. Your assessment of the flaws in this class might be correct, but there might not be anything I can do about it without breaking the class. That said, there is still a lot of room for small tweaks, and maybe there's some fundamental change I could make that would considerably improve things without sacrificing the concept.

Something else to keep in mind is that it's not necessarily as simple as comparing this to another class. You could play a fighter instead, for example, but you could also play a fighter and get an airship. If you play as this class, you're probably not going to get an airship, because you'll be the airship. If the DM doesn't let you get an airship, then they probably won't allow this class, either, for exactly the same reasons. It's kind of similar to how in isolation the monk's unarmored AC might look impressive with max DEX and WIS, but you can get the same AC with plate and a shield, so all it takes is a bit of gold to replicate that feature. So all the monk is really doing is saving some money. Likewise, some of the living dreadnought's features can be replicated just by buying the appropriate vehicle, allowing you to still gain those benefits even while playing a different class. Just something to remember when judging this class.